NEWS CENTER

Causes of Blocking of Raw Material Conveying Slant and Preventive Measures


Release time:

Feb 17,2012

1 conveying chute structure and characteristics of air conveying chute is an extraordinary form of continuous pneumatic conveying device, conveying dry powder material pneumatic conveying equipment, in the cement industry is often used to transport cement and raw material powder. The chute is widely used in conveying materials because there are no rotating parts, easy maintenance, good sealing, no noise, safe and reliable operation, low power consumption, convenient change of conveying direction, and multi-point feeding and multi-point unloading. The main body is connected by several sections of upper and lower two layers of grooves made of thin steel plates, which looks like a "day" from the cross section, as shown in Figure 1. Disposable ordinary sponge rubber skin for combination between each section

1 Conveying chute structure and characteristics

Air conveying chute is an extraordinary form of continuous pneumatic conveying device, conveying dry powder material pneumatic conveying equipment, in the cement industry is often used to transport cement and raw material powder. The chute is widely used in conveying materials because there are no rotating parts, easy maintenance, good sealing, no noise, safe and reliable operation, low power consumption, convenient change of conveying direction, and multi-point feeding and multi-point unloading. The main body is connected by several sections of upper and lower two layers of grooves made of thin steel plates, which looks like a "day" from the cross section, as shown in Figure 1. Each section is sealed with a "day" pad made of disposable ordinary sponge rubber skin, with a thickness of ≥ 10mm. The upper layer conveys materials, weighing the material passage, the lower layer passes high-pressure air, and is called the air passage. The height of the air passage is generally 1/5 of the height of the material passage. The breathable layer of polyester synthetic fiber fabric is used between the two layers, with a thickness of about 5mm. It has the advantages of high temperature resistance (≥ 150 ℃), corrosion resistance, wear resistance, low moisture absorption, light weight, smooth surface, long service life, etc. The device is only suitable for conveying material powder forward and downward, with a slope ≥ 8 °. In the case of process arrangement, a larger slope is beneficial to conveying.

2 Working principle

When conveying materials in the chute, the high-pressure air blown by the blower enters the air duct groove from the air inlet through the air duct to overcome the resistance between the air permeable layer and the material layer. The powdery materials are fluidized on the air permeable layer by filling the gaps between the powder particles with a certain flow rate. Due to the inclined arrangement of the chute, the fluidized powdery materials flow from high to low under the action of gravity to complete the material conveying.

3 Problems in production and use

Our company's new dry production line for 5,000 t/d cement clinker is equipped with RMR57/28-555 vertical raw material mill. The raw material from the mill is put into storage through XC630 × 79 500mm,8 inclination conveying chute. The conveying long chute is equipped with 2 fans (9-19No5.6 A, motor Y160L-2-18.5 kW). The phenomenon of blockage of the long chute for raw material conveying occurred at the beginning of production. It is difficult to handle and takes up to 2~5 h. In addition to blowing and blocking with compressed air forward, the wet material also needs to be cleaned and tamped out manually, which not only causes environmental pollution, but also wastes manpower and material resources, affects production and increases costs.

4 causes and prevention of blockage

Conveying chute aggregate blockage due to wet 4.1

4.1.1 Wet bottom of humidifying tower

At the initial stage of production, due to the lack of a supporting pure low-heat waste heat power generation project, when the raw meal mill is used for peak avoidance or spot inspection, the humidification tower is not properly sprayed with water to wet the bottom: when the raw meal mill is stopped, the humidification tower sprays water to cool down when the rotary kiln is ready for feeding or just stopping. At this time, there is no ash return in the high-temperature exhaust gas at the end of the kiln, and part of the kiln is vaporized by the hot air, the other part of the water vapor that has not evaporated falls into the wet bottom at the bottom of the humidification tower; when the humidification tower sprays water to cool down, the spray volume is too small to be atomized or the spray gun is damaged, and some water flows directly into the wet bottom of the humidification tower without atomization. This wet bottom return ash causes clogging of aggregate at the chute mouth of the conveyor chute, or clogging after a certain distance in the chute. Preventive measures: check the atomization effect of spray gun frequently at ordinary times. according to working experience, give appropriate water spray amount. when there is no ash-returning material in the high-temperature exhaust gas at the kiln tail and the temperature is high, open the cold air valve at the inlet of the dust collector and stop the water pump intermittently. this not only ensures the inlet temperature of the dust collector, but also ensures that all the water vapor entering the humidification tower is vaporized by the hot air flow, ensuring the humidity of the chute and safe transportation.

4.1.2 Caused by rain

Every rainy day, especially when it rains heavily in summer, the raw meal mill is driven and the chute is transported normally. Once the stock of raw meal is high, the high-priced electricity of the raw meal mill is used to avoid peaks or spot checks, the back ash material transported by the chute is easily blocked. After finding out the reasons, the following situations are found:

(1) The top of the vertical mill cyclone separator is ground through a number of small holes during long-term operation. Rainwater enters the raw material conveying system through these holes. Part of the wet material soaked by rainwater causes blockage of the cyclone separator and the long chute for raw material conveying. Preventive measures: seal the holes at the top of the cyclone separator and regularly check the loopholes to prevent rainwater from entering the cyclone separator system. In order to prevent rainwater from entering the cyclone separator system from loopholes that are not easy to observe, the vertical mill system is opened before it rains. Even if rainwater enters the raw material conveying system, the rainwater can be evaporated under the heat evaporation of a large amount of finished raw material without causing blockage. When the stock of raw material is extremely high or the inspection is not over, open the hot air valve into the mill by 50%, and hot air at about 80 ℃ passes through the cyclone separator of the vertical mill to evaporate the leaked rainwater.

(2) Leakage of the bag dust collector at the end of the kiln. The fitter renewed the worn cloth bag several times, piled up the aggregate in the worn cloth bag on the dust collector, blocked the drain outlet, damaged the sealing strip of the upper cover, rainwater entered the lake material in the individual cloth bag, and the wet material entered the chute opening of the conveying chute to block it after being discharged. Preventive measures are: clean up the collected materials or other sundries on the dust collector to ensure smooth drainage in rainy days, check the sealing of each cover plate, replace the damaged sealing strip with a new one, and avoid water ingress.

(3) Conveying the ash return in the middle of the long chute. There is a small bag dust collector around the elevator transfer building and the tail storage elevator. The situation and preventive measures they encounter are the same as the bag dust collector at the end of the kiln.

Conveying chute aggregate blockage caused by ash feeding in 4.2 air duct

4.2.1 Breathable layer damage

During installation of the chute, the construction team accidentally burned the breathable layer during electric welding; when the chute aggregate is blocked, the compressed air steel pipe head will wear the breathable layer. The above two situations can cause materials to enter the air duct from the gap of the breathable layer, resulting in reduced air volume in the air duct, blockage of the air duct, destruction of the flow state of the return ash material on the breathable layer, and blockage of the chute aggregate. Therefore, the breathable layer must be replaced. Bend the head of the compressed air steel pipe slightly when it is blocked again, and the elbow can be upward to avoid wearing the breathable layer.

4.2.2 "Day" pad damage

50~70 ℃ raw meal powder plus raw meal mill high-priced electricity to avoid peaks or stop for spot inspection, the kiln tail (≥ 160 ℃) high-temperature return ash material is transported for a long time, causing the "day" pad to be heated and deteriorated for a long time, and finally it is blown through by high-pressure wind. The material enters the air duct from the blowing through place, which also blocks the air duct, the compressed air steel pipe head will wear the "day" pad, and the above two conditions will cause the chute aggregate blockage as the damage of the breathable layer. The "day" pad in this section must be replaced with a new one. Similarly, use compressed air steel pipe with elbow to block, and the elbow can be upward to avoid wearing the "day" pad. In the above situation, one spare fan of the same type as the first two can be added to the lower half of the long chute to be turned on, and a Ф 1.5-inch ventilation pipe can be added to the air duct at the rear of the chute, so as to meet the ventilation requirements of the chute, and the excess air volume can blow the aggregate in the air duct from the rear of the chute. This measure is generally not advocated, which is not conducive to environmental health, but also increase the work of an 18.5kW fan, increase costs, resulting in waste. 5 Conclusion The blockage of the above several situations does not occur during the operation of the raw meal mill, because the conveying chute is 79,500mm long, with an inclination of 8 degrees and a large strand of raw meal of about 450 t/h can punch through the aggregate and take it away. In addition, waste heat power generation was completed and put into operation in June 2008. The waste gas at the kiln end is about 200 ℃, the humidification tower does not need to spray water, and the waste gas can enter the bag dust collector at the kiln end without cooling. It is safer to open the cold valve by 20%.